Base station apparatuses may adopt beamforming for an adaptive array antenna to perform radio communication with a terminal apparatus.
An adaptive array antenna represents, for example, an array antenna in which a plurality of antenna elements are arranged and phases of signals input to the individual antenna elements are adaptively controlled according to the propagation environment so that the directivity of the antenna may be electrically changed. Furthermore, beamforming represents, for example, a technique for controlling the directivity of an antenna. With the beamforming, a base station apparatus is able to transmit a radio signal to a direction in which a terminal apparatus is present and receive a radio signal transmitted from the direction in which the terminal apparatus is present.
In a base station apparatus, for example, an analog element such as an amplifier may be arranged up to an input end of each antenna element. Phases of signals input to input ends of antenna elements may differ according to the difference in characteristics between analog elements. In such a case, for example, calibration may be performed in the base station apparatus. Calibration represents, for example, a phase correction technique for causing different phases of individual antenna elements to match. By such calibration, for example, phases of transmission signals at input ends of individual antenna elements are made to match, so that the accuracy of beamforming may be increased.
As such a technique, for example, in a scheduler, a calibration signal is generated at a carrier to which no data signal is allocated. A base band processor calculates a calibration vector value, based on the calibration signal and a reception signal based on the calibration signal received through a transmission path, calibrates a beam coefficient using the calibration vector value, and transmits a data signal to the transmission path.
With this technique, in a multicarrier wave communication system using a smart antenna, an improved calibration apparatus and method for control of the phase and size of signals may be provided.
Furthermore, an array antenna apparatus has been available in which for combining of signals from antenna elements, a combining circuit connected to a phase shifter (phase control circuit) extracts a calibration signal outside a reception band through a first filter that is connected in a branching manner to each reception system, and calibration is performed by calculating a phase deviation among the reception systems based on the extracted calibration signal.
With this technique, in an array antenna apparatus, a calibration operation corresponding to a change in characteristics caused by a temperature change or the like may be performed properly and accurately.
Examples of the related art include, for example, Japanese Laid-open Patent Publication Nos. 2006-166452 and 2003-234610.